There is a plan to write an app in rails with similar functionality to this website: https://zoptamo.com but there is nooo idea which framework should be a best choice for this one since it should be lightweight, stable and fast as possible even on older devices. Can anyone help?

@violet this is a big question with a lot of branches. The correct answer is "it depends" and on many things. Do you have more direct access to a technical person or programmer that can help you through this decision?